Publication number | US7123744 B2 |

Publication type | Grant |

Application number | US 10/305,192 |

Publication date | Oct 17, 2006 |

Filing date | Nov 27, 2002 |

Priority date | Nov 30, 2001 |

Fee status | Lapsed |

Also published as | CN1421830A, DE60222986D1, DE60222986T2, EP1321895A2, EP1321895A3, EP1321895B1, EP1643440A2, EP1643440A3, US20030108219 |

Publication number | 10305192, 305192, US 7123744 B2, US 7123744B2, US-B2-7123744, US7123744 B2, US7123744B2 |

Inventors | Hirofumi Muratani, Tooru Kambayashi, Tomoo Yamakage, Shinichiro Koto, Tomoya Kodama, Hisashi Yamada |

Original Assignee | Kabushiki Kaisha Toshiba |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (11), Non-Patent Citations (14), Referenced by (17), Classifications (14), Legal Events (4) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US 7123744 B2

Abstract

A digital watermark embedding apparatus comprises a digital watermark generating unit which transforms embedding target contents by using a filter having a coefficient with a periodic number sequence to generate a digital watermark, and an embedding unit which superposes the digital watermark on the embedding target contents to generate watermark embedded contents.

Claims(9)

1. A digital watermark embedding apparatus comprising:

a digital watermark generator which generates a digital watermark by transforming an embedding target content with a coefficient of a periodic number sequence; and

an embedding unit which embeds the digital watermark in the embedding target content;

wherein the periodic number sequence comprises a periodic pseudo-random number sequence;

wherein the digital watermark generator generates the following digital watermark F[p]

where p represents the embedding target content;

z represents a parameter assigning a component of the embedding target content p;

f_{y }represents the periodic pseudo-random number sequence; and

y represents an integer number expressing a number of a term of the periodic pseudo-random number sequence.

2. A digital watermark embedding method comprising:

generating a digital watermark by transforming an embedding target content with a coefficient of a periodic number sequence; and

embedding the digital watermark in the embedding target content;

wherein the periodic number sequence comprises a periodic pseudo-random number sequence;

wherein the digital watermark generating generates the following digital watermark F[p]

where p represents the embedding target content;

z represents a parameter assigning a component of the embedding target content p;

f_{y }represents the periodic pseudo-random number sequence; and

y represents an integer number expressing a number of a term of the periodic pseudo-random number sequence.

3. A digital watermark detecting apparatus comprising:

a transforming unit which transforms a detecting target content with a coefficient of a periodic number sequence;

a first cross-correlation calculator which calculates a first cross-correlation between the transformation result and the detecting target content;

an auto-correlation calculator which calculates an auto-correlation of the first cross-correlation;

a scaling rate calculator which calculates a scaling rate based on a peak position of the auto-correlation and a period of the periodic number sequence;

a scaling unit which scales one of the first cross-correlation and the periodic number sequence;

a second cross-correlation calculator which calculates a second cross-correlation between the first cross-correlation scaled and the periodic number sequence not scaled or between the first cross-correlation not scaled and the periodic number sequence scaled; and

a detector which detects whether a digital watermark is embedded in the detecting target contents based on the second cross-correlation.

4. The apparatus according to claim 3 , wherein the periodic number sequence comprises a periodic pseudo-random number sequence.

5. The apparatus according to claim 4 , wherein the first cross-correlation calculator calculates the following first cross-correlation C(Δ1)

*C*(Δ1)=*p′*G* _{66 } *[p′]*

where p′ represents the detecting target content; and GΔ[p′] represents the transformation result; and

said auto-correlation calculator calculates the following auto-correlation Γ(P′)

where P′ represents a peak position of the auto-correlation.

6. A digital watermark detecting method comprising:

transforming a detecting target content with a coefficient of a periodic number sequence;

calculating a first cross-correlation between the transformation result and the detecting target content;

calculating an auto-correlation of the first cross-correlation;

calculating a scaling rate based on a peak position of the auto-correlation and a period of the periodic number sequence;

scaling one of the first cross-correlation and the periodic number sequence;

calculating a second cross-correlation between the first cross-correlation scaled and the periodic number sequence not scaled or between the first cross-correlation not scaled and the periodic number sequence scaled; and

detecting whether a digital watermark is embedded in the detecting target content based on the second cross-correlation.

7. The method according to claim 6 , wherein the periodic number sequence comprises a periodic pseudo-random number sequence.

8. The method according to claim 7 , wherein the first cross-correlation comprises the following first cross-correlation C(Δ1)

*C*(Δ1)=*p′*G* _{66 } *[p′]*

where p′ represents the detecting target content; and G_{66}[p′] represents the transformation result; and

said auto-correlation comprises the following auto-correlation Γ(P′)

where P′ represents a peak position of the auto-correlation.

9. A computer program product, having instructions that when executed by a processor perform steps comprising:

transforming a detecting target content with a coefficient of a periodic number sequence;

calculating a first cross-correlation between the transformation result and the detecting target content;

calculating an auto-correlation of the first cross-correlation;

calculating a scaling rate based on a peak position of the auto-correlation and a period of the periodic number sequence;

scaling one of the first cross-correlation and the periodic number sequence;

calculating a second cross-correlation between the first cross-correlation scaled and the periodic number sequence not scaled or between the first cross-correlation not scaled and the periodic number sequence scaled; and

detecting whether a digital watermark is embedded in the detecting target content based on the second cross-correlation.

Description

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-367944, filed Nov. 30, 2001, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a digital watermark embedding method, a digital watermark embedding apparatus, a digital watermark detecting method, and a digital watermark detecting apparatus.

2. Description of the Related Art

Popularization of apparatuses for recording and reproducing digital image data such as digital video cassette recorders and DVD (digital versatile disk) systems results in offers of various digital moving picture images which can be reproduced by the apparatus. Furthermore, various digital moving picture images are distributed through digital television broadcasting by using internet, broadcasting satellite, and communication satellite, so that it is being possible for users to use the high quality digital moving picture images.

In the digital moving picture image, since high quality duplicate can be easily produced at a state of a digital signal level, it is a danger of the unlimited duplicate in case that duplicate prohibition or duplicate control is not given. Accordingly, in order to prevent illegal duplicate of the digital moving picture image or in order to control a generation number of the duplicate by normal users, a method for limiting the duplicate, which information for the duplicate control is added to the digital moving picture image and the illegal duplicate is prevented by using the additional information, has been proposed.

The digital watermark is known as a technique which superposes other additional information on the digital moving picture image. In the digital watermarking technique, information (referred to as “watermark information”) such as identifying information of a copyright holder or a user of contents, information of right of the copyright holder, a condition of utilization of the contents, secret information necessary for utilizing, or the above-described information of the duplicate control is embedded on digital contents such as digitalized data of sound, music, moving picture image, and static picture image such that it is not easy to perceive the information. Then, by detecting the watermark information from the embedded contents if necessary, protection of the copyright containing utilizing control and the duplicate control or promotion of secondary utilization can be performed.

Generally, the digital contents express as a set of a plurality of digital data which is a component of the digital contents. For example, in case that the digital contents are a digital image, the digital contents include a set of pixels. The digital contents are expressed as p=(p(z)). Where z of the contents should be a parameter showing a position of the component (for example, pixel), and p(z) should express a data value (for example, pixel value) of the component of the position z.

The digital watermark means other data which are embedded in the contents by varying the data value of one or more components in the contents. As shown generally in the following equation (1), embedding of the digital watermark generates data F[p] having which embedding target contents p is carried out by a transformation F and superposes the data F[p] on the embedding target contents p, which allows embedded contents E[p] to be produced.

*E[p]=p+F[p]* (1)

On the other hand, detection of the embedded digital watermark generates data G[p′] which detecting target contents p′ is carried out by a transformation G and carries out whether cross-correlation between the data G[p′] and the detecting target contents p′ exceeds a certain threshold value Th_{1 }or not.

That is,

*D[p′]=θ*(*p′*G[p′]−Th* _{1}) (3)

where θ(x) is 1 in case of x≧0 (deciding that the digital watermark is in the detecting target contents), and θ(x) is 0 and a step function in case of x<0 (deciding that the digital watermark is not in the detecting target contents), so that a detecting result D[p′] is obtained according to the step function. The transformation G in detecting may be the same as the transformation F in embedding for simplifying.

Scaling is one of typical attacks for erasing or altering the digital watermark (enlargement or reduction in case of the image). When the scaling is carried out, the parameter z assigning the component of the contents is transformed under the scaling of a scaling rate α as follows:

*z *

where, z

For this reason, the watermark can not be detected even though the transformation G is carried out to find the cross-correlation.

A method called “echo hiding” which is a digital watermarking technique for music is known as a digital watermarking method being robust against the scaling (W. Bender, D. Gruhl, N. Morimoto and A. Lu, “Techniques for data hiding”, IBM Systems Journal, Vol. 35, Nos. 3&4, 313–336, 1996.: hereinafter referred to as “the reference”).

*F[p]*(*z*)=*p*(*z*+δ)

*G[p]*(*z*)=*p′*(*z+Δ*) (5)

That is, the parameter z is shifted by δ in case of embedding the digital watermark, and the parameter z is shifted by Δ in case of detecting the digital watermark. In this method, because detection is carried out by varying a value of Δ during detecting the digital watermark, even though the parameter z is transformed by scaling, the detecting result D[p′] of the digital watermark outputs “1” in case of Δ=αδ, namely it is expected that there is a decision that the digital watermark is in the detecting target contents.

However, the reference is not effective in a digital watermark embedding/detecting method in which auto-correlation of the embedded contents has a peak. This is because once an outsider has learned the digital watermark embedding/detecting method, by analyzing whether or not the remarkable (unnatural) peak exists in the auto-correlation, the outsider determines whether or not the digital watermark is in the contents to erase or alter easily the digital watermark. Accordingly, it is desirable to realize a digital watermark embedding/detecting method not having a remarkable peak in the auto-correlation and being robust against the scaling.

The present invention is directed to method and apparatus that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

It is an object of the present invention to provide a digital watermark embedding method, a digital watermark embedding apparatus, a digital watermark detecting method, and a digital watermark detecting apparatus which can correctly detect embedded digital watermark information even when the embedded digital watermark information is scaled and which it is hardly found whether or not the digital watermark is in the embedded contents.

According to an embodiment of the present invention, a digital watermark embedding apparatus comprises:

a digital watermark generator which generates a digital watermark by transforming an embedding target content with a coefficient of a periodic number sequence; and

an embedding unit which embeds the digital watermark in the embedding target content.

According to an embodiment of the present invention, a digital watermark embedding method comprises:

generating a digital watermark by transforming an embedding target content with a coefficient of a periodic number sequence; and

embedding the digital watermark in the embedding target content.

According to an embodiment of the present invention, a digital watermark detecting apparatus comprises:

a transforming unit which transforms a detecting target content with a coefficient of a periodic number sequence;

a first cross-correlation calculator which calculates a first cross-correlation between the transformation result and the detecting target content;

an auto-correlation calculator which calculates an auto-correlation of the first cross-correlation;

a scaling rate calculator which calculates a scaling rate based on a peak position of the auto-correlation and a period of the periodic number sequence;

a scaling unit which scales one of the first cross-correlation and the periodic number sequence;

a second cross-correlation calculator which calculates a second cross-correlation between the first cross-correlation scaled and the periodic number sequence not scaled or between the first cross-correlation not scaled and the periodic number sequence scaled; and

a detector which detects whether a digital watermark is embedded in the detecting target contents based on the second cross-correlation.

According to an embodiment of the present invention, a digital watermark detecting method comprising:

transforming a detecting target content with a coefficient of a periodic number sequence;

calculating a first cross-correlation between the transformation result and the detecting target content;

calculating an auto-correlation of the first cross-correlation;

calculating a scaling rate based on a peak position of the auto-correlation and a period of the periodic number sequence;

scaling one of the first cross-correlation and the periodic number sequence;

calculating a second cross-correlation between the first cross-correlation scaled and the periodic number sequence not scaled or between the first cross-correlation not scaled and the periodic number sequence scaled; and

detecting whether a digital watermark is embedded in the detecting target content based on the second cross-correlation.

**31** in

**43** in

**35** in

**37** in

An embodiment of a digital watermark embedding apparatus and a digital watermark detecting apparatus according to the present invention will now be described with reference to the accompanying drawings.

**10**, in which watermark information should be embedded (hereinafter referred to “embedding target contents”), to the digital watermark embedding apparatus.

The embedding target contents **10** are input to a digital watermark generating unit **11** and a embedding unit **15**. In the digital watermark generating unit **11**, a transformation based on a periodic number sequence **13** (in this embodiment, a periodic pseudo-random number sequence) generated by a pseudo-random number generating unit **12** is carried out for the embedding target contents **10** to generate a digital watermark **14** to be embedded in the embedding target contents **10**. The pseudo-random number sequence **13** is a sequence that a bit of “0” and a bit of “1” generate in random, the sequence is to be repeatedly generated in a certain period. The pseudo-random number sequence **13** is treated as a secret key and is not in public.

In the embedding unit **15**, contents **16** in which the watermark information has been embedded (hereinafter referred to as “embedded content”) are generated by embedding the digital watermark **14** in the embedding target contents **10**. The embedded contents **16** generated in the above-described way are recorded in a recording medium by a digital image recording and reproducing apparatus such as a DVD system or transmitted through a transmission medium such as the internet, the broadcasting satellite, and the communication satellite.

The digital watermark generating unit **11** will be described in more detail below. In the digital watermark generating unit **11**, a transformation shown in the following equation (6) is carried out to generate the pseudo-random number sequence **13**:

where F[p] represents a digital watermark; p represents embedding target contents; z represents a parameter assigning a component of the embedding target contents p; f_{y }represents a periodic pseudo-random number sequence; and y represents an integer number expressing a number of a term of the periodic pseudo-random number sequence.

That is, in the example of the reference described above, the following equation (7) is correspondent to f_{y }in the equation (6):

However, in the embodiment, as shown in the following equation (8), f_{y }is the pseudo-random number sequence (for example, a sequence following Gaussian distribution) having a period P:

*f* _{i} *∈N*(σ,0)

*f* _{i+P} *=f* _{i} (8)

where, σ expresses dispersion in the Gaussian distribution.

**11** calculating the equation (6).

The digital watermark generating unit **11** _{j }includes a multiplying unit **21** _{i }provided corresponding to each i calculating a product of an (i+j)-th component **10** _{i+j }of the embedding target contents by an i-th component **13** _{i }of the pseudo-random number sequence **13** and an adding unit **22** adding an output of the multiplying unit **21** _{i }correspondent to all the i's to output a j-th component **14** _{j }of the digital watermark **14**, which is provided corresponding to each j, consequently the digital watermark generating unit **11** is arranged.

On the other hand, the embedding unit **15** in **16** whose component is that the digital watermark **14** output from the digital watermark generating unit **11** and the embedding target contents **10** are added in every component. The digital watermark **14** may be embedded in the embedding target contents **10** after multiplying the digital watermark **14** by a properly minute factor such that the digital watermark **14** is more inconspicuous than the component of the embedding target contents **10**.

When the embedded contents **16** in which the digital watermark is embedded is generated by embedding the watermark information, as described below, the watermark information which is embedded as the digital watermark in the embedded contents **16** can be certainly detected even when the embedded contents **16** is scaled (enlargement or reduction in case that the embedded contents **16** is an image).

The embedded contents **16** generated in the above-described way does not show a remarkable peak in the auto-correlation, because, as shown in the equation (6), the digital watermark **14** generated by the transformation with a coefficient of the periodic pseudo-random number sequence **13** for the embedding target contents **10** is embedded in the embedding target contents **10**. Accordingly, the embedded contents **16** is robust against peak analysis of the auto-correlation by a hacker who tries to alter or erase the digital watermark **14**, so that the embedded contents **16** has an advantage that it is hardly found whether or not the digital watermark is in the embedded contents **16** by the hacker.

**30** from which the embedded watermark information should be detected (hereinafter referred to as “detecting target contents”) are input to the digital watermark detecting apparatus.

There are a case which the embedded contents **16** generated by the digital watermark embedding apparatus shown in **30** are generally a kind of contents which is unknown whether the digital watermark is embedded or not. The digital watermark detecting apparatus can also detect whether or not the digital watermark is embedded with respect to the embedded contents **16** in which, as described above, the peak of the auto-correlation is not clearly appeared.

In **30** are input to a cross-correlation calculating unit **31**. A pseudo-random number sequence **33** generated by a pseudo-random number generating unit **32** is also input to the cross-correlation calculating unit **31**. The pseudo-random number generating unit **32** generates the periodic pseudo-random number sequence **33** which is the same as the pseudo-random number sequence **13** generated by the pseudo-random number generating unit **12** in the digital watermark embedding apparatus shown in **33** is also treated as the secret key and is not in public. The cross-correlation calculating unit **31** generates a result which is obtained by transforming the detecting target contents **30** with a coefficient of the pseudo-random number sequence **33** generated by the pseudo-random number generating unit **32** and a first cross-correlation value **34** which is obtained by calculating cross-correlation to the detecting target contents **30**.

A process in the cross-correlation calculating unit **31** comprises two steps, that is, a first step of transforming the detecting target contents **30** with the coefficient of the periodic pseudo-random number sequence **33** and a second step of calculating the cross-correlation between the result of the transformation in the first step and the detecting target contents **30** to generate the first cross-correlation value **34**.

The first cross-correlation value **34** output from the cross-correlation calculating unit **31** is input to an auto-correlation calculating unit **35** and a digital watermark detecting unit **37**. In the auto-correlation calculating unit **35**, auto-correlation of the first cross-correlation value **34** is calculated to generate an auto-correlation value **36**.

The digital watermark detecting unit **37** scales the first cross-correlation value **34** by a scaling rate to the detecting target contents **30** which is calculated by a peak position of the auto-correlation value **36**, and determines whether or not the watermark information is in the detecting target contents **30** by judging a threshold value with respect to a second cross-correlation value which is generated by calculating the cross-correlation between the scaled first cross-correlation value and the pseudo-random number sequence **33**. The scaling rate expresses a degree of the scaling in case that the detecting target contents **30** (for example, the embedded contents **16**) are scaled, the scaling rate is an enlargement rate or a reduction rate in case that the contents are the image.

A process in the digital watermark detecting unit **37** comprises four steps, that is, a first step of calculating the scaling rate to the detecting target contents **30** from the peak position of the auto-correlation value **36**, a second step of scaling the first cross-correlation value **34** by the calculated scaling rate, a third step of generating the second cross-correlation value by calculating the cross-correlation between the scaled cross-correlation value and the pseudo-random number sequence **33**, and a fourth step of determining whether or not the watermark information is in the detecting target contents **30** by judging the threshold value with respect to the second cross-correlation value.

The above-described process of the digital watermark detecting apparatus according to the embodiment will be described below in more detail with reference to a flow chart shown in

In the cross-correlation calculating unit **31**, as shown in the following equation (9), the first cross-correlation between the result of the transformation to the detecting target contents **30** with the coefficient of the periodic pseudo-random number sequence **33** and the detecting target contents **30** is calculated (step S**12**):

*C*(Δ1)=*p′*G* _{Δ} *[p′]* (9)

where C(Δ**1**) represents the first cross-correlation value **34**; p′ represents the detecting target contents **30**; and G_{Δ}[p′] represents a result of transformation by a filter with a coefficient of the periodic pseudo-random number sequence **33**.

In the auto-correlation calculating unit **35**, as shown in the following equation (10), the auto-correlation with respect to the first cross-correlation value C(Δ**1**) shown in the equation (9) is calculated (step S**14**):

where Γ(P′) represents the auto-correlation value **36**; and P′ represents a peak position of the auto-correlation value **36**. Thus, the peak is appeared every period P′ in the auto-correlation value ΓF(P′).

In the digital watermark detecting unit **37**, the following process is carried out.

The peak position P′ (period) of the auto-correlation value Γ(P′) satisfies the following equation (11) between a period P and a scaling rate α of the pseudo-random number sequence **33**.

When the detecting target contents **30** is not scaled, that is, α=1, the peak position P′ is equal to the period P of the pseudo-random number sequence **33**. For this reason, in the digital watermark detecting unit **37**, first the peak position P′ of the auto-correlation value Γ(P′) is detected (step S**16**), and then the scaling rate α is calculated by the equation (11) (step S**18**).

The digital watermark detecting unit **37** scales the first cross-correlation value C(Δ**1**) by using the calculated scaling rate α to generate the scaled cross-correlation value (step S**20**). Then, the digital watermark detecting unit **37** calculates the cross-correlation between the scaled cross-correlation value and the pseudo-random number sequence **33** according to the following equation (12) to generate the second cross-correlation value (step S**22**):

where C(Δ**2**) represents the second cross-correlation value; f_{i }represents the periodic pseudo-random number sequence **33**; and C(iα) represents the scaled cross-correlation value.

Finally, the digital watermark detecting unit **37** carries out the decision of the threshold value (Th_{2}) with respect to the second cross-correlation value C(Δ**1**) shown in the equation (12) by using the following relation (**13**) (steps S**24** to S**28**):

*C*(Δ2)>*Th* _{2} (13)

so as to output a detecting result of the digital watermark **38**. This allows the decision of the digital watermark based on the correct peak position P′ to be done, even when a plurality of peaks are appeared in the auto-correlation value **36**.

When the outsider (hacker) tries to alter or erase the digital watermark in the embedded contents **16** which is generated by the digital watermark embedding apparatus shown in **13** used in embedding and the pseudo-random number sequence **33** used in detecting with the digital watermark detecting apparatus are the secret key and the hacker does not know the secret key. Since the many peaks of the auto-correlation value generate in random according to the pseudo-random number sequence, the hacker can not recognize the remarkable peak. Consequently, the embedded contents **16** in which the digital watermark is embedded by the digital watermark embedding apparatus shown in

A detail arrangement of each part of

**31** in **31** includes a digital watermark generating unit **41** and a correlation calculating unit **43** and carries out the calculation shown in the equation (9). The digital watermark generating unit **41** is configured, as shown in **11** of the digital watermark embedding apparatus shown in **33** which is generated with respect to the detecting target contents **30** by the pseudo-random number generating unit **32**. As a result of the transformation, the digital watermark generating unit **41** synthesizes a digital watermark **42** corresponding to the digital watermark **14** which is embedded in the embedding target contents **10**. The correlation calculating unit **43** calculates the cross-correlation between the digital watermark **42** and the detecting target contents **30** to generate the first cross-correlation value **34**.

**43** shown in **43** _{j }includes a multiplying unit **51** _{i }provided corresponding to each i calculating a product of an i-th component **30** _{i }of the detecting target contents **30** by an (i+j)-th component **42** _{i+j }of the digital watermark **42** and an adding unit **52** adding an output of the multiplying unit **51** _{i }correspondent to all the i's to output a j-th component **34** _{j }of the cross-correlation value **34**, which is provided corresponding to each j, consequently the correlation calculating unit **43** is arranged.

**35** shown in **35** includes a correlation calculating unit **60** having the same arrangement shown in **43** in the auto-correlation calculating unit **35** in **30** and the digital watermark **42** in **34** is commonly input to two inputs of the correlation calculating unit **60**, so that the process shown in the equation (10) is carried out to output the auto-correlation value **36**.

**37** shown in **37** includes a peak detecting unit **71**, a scaling unit **72**, a correlation calculating unit **73**, and a threshold value decision unit **74**, and carries out processes shown in the equations (11), (12), and (13).

The peak detecting unit **71** detects the peak position P′ of the auto-correlation value **36** from the auto-correlation calculating unit **35**, and then the scaling unit **72** scales the second cross-correlation value **34** according to the scaling rate α calculated by the equation (11) with the period P of the pseudo-random number sequence **33** which is given beforehand and the peak position P′. In the correlation calculating unit **73**, the cross-correlation between the scaled correlation value and the periodic pseudo-random number sequence **33** is calculated by the equation (12), the second cross-correlation value which is a 0-th component of the cross-correlation is obtained. The threshold value decision shown in the equation (13) is carried out with respect to the second cross-correlation value in the threshold value decision unit **74**. The threshold value decision unit **74** decides that the watermark information is embedded in the detecting target contents **30** when the second cross-correlation value exceeds the threshold value Th_{2}, and decides that the watermark information is not embedded in other cases, and the decision result is output as the digital watermark detecting result **38**.

As described above, in the digital watermark embedding apparatus according to the first embodiment, the embedded contents **16** are generated in a manner that the result which the embedding target contents **10** is transformed by the filter with the coefficient of the periodic pseudo-random number sequence **13** is embedded in the embedding target contents **14**.

In the digital watermark detecting apparatus, the scaling rate α for the detecting target contents is calculated from the peak position P′ of the auto-correlation value **36** of the first cross-correlation value **34**, which is generated by calculating the cross-correlation between the result which the detecting target contents **30** is transformed by the filter with the coefficient of the periodic pseudo-random number sequence **33** and the detecting target contents **30**, and the period P of the periodic pseudo-random number sequence **33**. After the first cross-correlation value **34** is scaled by the scaling rate α, the threshold value decision is carried out with respect to the second cross-correlation value generated by calculating the cross-correlation with the periodic pseudo-random number sequence **33**. Consequently, it is determined whether or not the watermark information is in the detecting target contents **30**.

The digital watermark can be detected even when the embedded contents **16** is scaled, robust characteristics against the scaling can be obtained. The peaks of the auto-correlation are randomized and the remarkable peak in the auto-correlation is not appeared because the result of the transformation by a filter with the coefficient of the periodic pseudo-random number sequence **13** is embedded in the embedding target contents **10** in the digital watermark embedding apparatus. Accordingly, it is difficult for the hacker to detect the peak to determine whether or not the digital watermark is in the embedded contents **16**, which enable the embedded contents **16** to be robust against the alteration or the erase of the digital watermark. Furthermore, by using the periodic pseudo-random number sequence as the secret key, it is impossible to calculate the equations (9) and (10) even though the digital watermark embedding algorithm is leaked out, so that the alteration or the erase of the embedded digital watermark can not be carried out.

Other embodiments of the present invention will be described. The same portions as those of the first embodiment will be indicated in the same reference numerals and their detailed description will be omitted.

In the first embodiment, there is described the case in which the watermark information of one bit is embedded by the digital watermark embedding apparatus and the digital watermark detecting apparatus determines whether or not the watermark information is in the embedded contents. As described below, the present invention can be also applied to a digital watermark embedding apparatus and a digital watermark detecting apparatus which process watermark information of multi-bit.

**17** _{1 }to **17** _{N }(N is plural number). The digital watermark embedding apparatus includes the N-number of digital watermark embedding units **8** _{1 }to **8** _{N}, wherein the digital watermark embedding apparatus including the digital watermark generating unit **11**, the pseudo-random number generating unit **12**, and the embedding unit **15** in **10** are commonly input to the digital watermark embedding units **8** _{1 }to **8** _{N}.

The watermark information of N bits **17** _{1 }to **17** _{N }are input to the pseudo-random number generating units **12** in the digital watermark embedding units **8** _{1 }to **8** _{N }respectively. Each pseudo-random number generating unit **12** generates the different pseudo-random number sequence according to, for example, each bit value (“0” or “1”) of the watermark information of N bits **17** _{1 }to **17** _{N}. In another example, the pseudo-random number generating unit **12** may generate the pseudo-random number sequence having a reverse polarity according to each bit value of the watermark information of N bits **17** _{1 }to **17** _{N}. Furthermore, the pseudo-random number generating units **12** may generate the pseudo-random number sequence or a sequence having all “0” (which corresponds to not embedding) according to each bit value of the watermark information of N bits **17** _{1 }to **17** _{N}.

In the digital watermark embedding units **8** _{1 }to **8** _{N}, after the digital watermark is embedded in the embedding target contents **10** by the same process as the first embodiment, the embedded contents **16** in which the watermark information of N bits is embedded is generated by adding outputs of the digital watermark embedding units **8** _{1 }to **8** _{N }in an adding unit **18**. When the embedded contents **16** is generated in this way, the embedded watermark information of N bits can be securely detected in the same way as the first embodiment even when the embedded contents **16** is scaled.

**8** _{1 }to **8** _{N}, the digital watermark detecting apparatus includes a plurality of digital watermark detecting units **9** _{1 }to **9** _{N }wherein the digital watermark detecting apparatus including the cross-correlation calculating unit **31**, the pseudo-random number generating unit **32**, the auto-correlation calculating unit **35**, and the digital watermark detecting unit **37** in **30** is one digital watermark detecting unit. In the same way as the first embodiment, the detecting results **38** of the digital watermark are generated by the digital watermark detecting units **9** _{1 }to **9** _{N }the detecting results **38** as a whole are output as the detecting results of the digital watermark of the multi-bit.

According to the digital watermark embedding apparatus and the digital watermark detecting apparatus of the present invention, even when the embedded contents **16** are scaled in the same way as the first embodiment, the detecting results **38** of the digital watermark are not affected by the scaling and the embedded watermark information of N bits can be securely detected. There is also the same advantage as the first embodiment that the embedded contents **16** are robust against the attack such as the alteration or the erase of the digital watermark by outsider.

Procedure of the digital watermark embedding apparatus and the digital watermark detecting apparatus according to the above-described embodiments of the present invention can be carried out by not only hardware but also software.

Though the first cross-correlation value **34** is scaled during detecting the digital watermark in the above-described embodiments, the pseudo-random number sequence **33** may be scaled, it goes without saying that the same result as the scaling of the first cross-correlation value **34** can be obtained.

The periodic pseudo-random number sequence is used as the periodic sequence in the above-described embodiment. However, it is not always necessary to use the pseudo-random number sequence.

As described above, the digital watermark according to the embodiments of the present invention is robust against the scaling for the contents, the digital watermark embedding and digital watermark detecting can be stronger against the alteration or the erase of the digital watermark by the outsider.

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the present invention being indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. For example, the present invention can be practiced as a computer readable recording medium in which a program for allowing the computer to function as predetermined means, allowing the computer to realize a predetermined function, or allowing the computer to conduct predetermined means. The pseudo-random number sequence may be replaced by a number sequence whose auto-correlation has a periodic peak.

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Classifications

U.S. Classification | 382/100, 713/176 |

International Classification | H04N7/08, H04N1/387, G06K9/00, H04N7/081, G06T1/00 |

Cooperative Classification | G06T2201/0065, G06T1/005, G06T1/0064, G06T2201/0052, G06T2201/0083 |

European Classification | G06T1/00W6, G06T1/00W6G |

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Nov 27, 2002 | AS | Assignment | Owner name: KABUSHIKI KAISHA TOSHIBA, JAPAN Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MURATANI, HIROFUMI;KAMBAYASHI, TOORU;YAMAKAGE, TOMOO;ANDOTHERS;REEL/FRAME:013533/0815 Effective date: 20021121 |

May 24, 2010 | REMI | Maintenance fee reminder mailed | |

Oct 17, 2010 | LAPS | Lapse for failure to pay maintenance fees | |

Dec 7, 2010 | FP | Expired due to failure to pay maintenance fee | Effective date: 20101017 |

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